1. Field of the Invention
This invention relates to a printing machine that controls an ink feeding rate and a dampening water feeding rate by measuring the color density of prints produced.
2. Description of the Related Art
Such a printing machine includes ink feeders for adjusting the rates of feeding inks to ink rollers. Each ink feeder has a plurality of ink keys juxtaposed in a direction perpendicular to a direction for transporting printing paper in time of printing. The rate of feeding ink to the ink rollers is adjusted by varying the opening degree of each ink key. In this way, the rate of feeding ink ultimately to the printing plate is adjusted.
The printing machine further includes dampening water feeders for adjusting the rate of feeding dampening water to dampening form rollers. Each dampening water feeder includes a water source having a water vessel for storing dampening water and a fountain roller rotatable by a motor, and dampening form rollers for transferring dampening water from the fountain roller to the surface of the printing plate. Such a dampening water feeder can adjust the rate of feeding dampening water to the surface of the printing plate by varying the rotational frequency of the fountain roller.
The printing plate has regions called detecting patches or control strips formed in positions corresponding to the respective ink keys. The opening degree of each ink key and the rotational frequency of the water fountain roller are adjusted by measuring, with a densitometer, the color density of the corresponding detecting patch actually printed on printing paper.
In a printing operation of the printing machine, the color density of prints may not attain a predetermined value immediately after start of the printing operation even though the opening degree of each ink key in the ink feeder is proper. In such a case, when the color density of prints is measured and the feeding rates of ink and dampening water are automatically controlled, the opening degree of each ink key and the rotational frequency of the water fountain roller are further adjusted even though the feeding rates of ink and water are proper.
To avoid such a situation, adjustments of the opening degree of each ink key and the rotational frequency of the water fountain roller are prohibited immediately after start of a printing operation, or until a predetermined number of sheets are printed or until elapse of a fixed time after the feeding rate of ink or dampening water is adjusted.
However, where a long prohibition time is set for prohibiting adjustment of the opening degree of each ink key until a predetermined number of sheets are printed or until elapse of a fixed time after the feeding rate of ink or dampening water is adjusted, the feeding rate of ink or dampening water cannot be controlled quickly. This results in the inconvenience of consuming a long time before the color density of prints actually produced attains a target value.
The object of this invention, therefore, is to provide a printing machine for allowing the color density of prints to attain a target value quickly by appropriately controlling a prohibition time for prohibiting variations in the feeding rate of ink or dampening water.
The above object is fulfilled, according to this invention, by a printing machine for controlling an ink feeding rate and a dampening water feeding rate by measuring color density of prints produced, wherein, after a variation in one of the ink feeding rate and the dampening water feeding rate, a variation in the ink feeding rate or the dampening water feeding rate is prohibited for a predetermined waiting period.
This printing machine appropriately controls a prohibition time for prohibiting a variation in the ink feeding rate or dampening water feeding rate. This effectively avoids the above-noted inconvenience of consuming a long time before the color density of actual prints attains a target value.
In one preferred embodiment, the waiting period is determined by a set-number-of-sheets printing time required for printing a predetermined number of sheets of printing paper.
Preferably, the waiting period is determined based on a pattern area rate of a pattern to be printed.
The waiting period may be extended when the pattern area rate is less than a predetermined value.
In a further preferred embodiment, after a variation in one of the ink feeding rate and the dampening water feeding rate, a variation in the ink feeding rate is prohibited for a set-number-of-sheets printing time required for printing a predetermined number of sheets of printing paper.
Other features and advantages of the present invention will be apparent from the following detailed description of the embodiments of the invention.